So the long hair for women thing is based on several reasons
Long hair is considered attractive full stop. It's pleasing on all genders across all cultures but it is also impractical for manual labour, fighting, hunting ect. In most primitive societies and even in many modern societies men prioritize work and woman prioritize beauty. So that's why we get the long hair for women thing and to some extent short hair for men, it's about gender roles and how we like people who live up to them.
This has little to do with sexual attraction, it is more about social acceptance. That's why people are able to find a woman with short hair attractive or a man with long hair attractive even in an incredibly patriarchal society.
Yes people decide what culture is and that is informed by biology but that doesn't mean that cultural standards are somehow biological standards.